Motor drive apparatus capable of accurately estimating demagnetization of permanent magnet motor

ABSTRACT

A map holding unit holds, in the form of a map, a voltage control amount of the q axis in a case where no demagnetization of a permanent magnet motor occurs. Based on a motor revolution number, namely the number of revolutions of the motor provided from a revolution number detection unit, a demagnetized state calculation unit calculates a rotational angular velocity. Then, based on the voltage control amount from the map holding unit, a voltage control amount to be controlled that is provided from a PI control unit and the rotational angular velocity, the demagnetized state calculation unit calculates an amount of demagnetization and outputs, if the amount of demagnetization is greater than a predetermined value, an operation signal for controlling the operation of the permanent magnet motor.

TECHNICAL FIELD

The present invention relates to a motor drive apparatus capable ofestimating demagnetization of a permanent magnet motor.

BACKGROUND ART

Hybrid vehicles have recently been of great interest asenvironment-friendly vehicles. The hybrid vehicles are now partiallycommercialized.

A hybrid vehicle has, as its motive power sources, a DC (direct current)power supply, an inverter and a motor driven by the inverter in additionto a conventional engine. More specifically, the engine is driven tosecure the motive power source and a DC voltage from the DC power supplyis converted by the inverter into an AC voltage to be used for rotatingthe motor and thereby securing the motive power source as well.

Japanese Patent Laying-Open No. 2001-157304 discloses a motor drivesystem for a hybrid vehicle. The motor drive system estimatesdemagnetization of a permanent magnet of an electric rotating machinefrom the temperature of the permanent magnet according to data used forcontrolling the hybrid vehicle.

The conventional method, however, estimates demagnetization from thetemperature of the permanent magnet which is estimated according to thecontrol data for the hybrid vehicle, resulting in a problem that thedemagnetization cannot accurately be estimated.

DISCLOSURE OF THE INVENTION

An object of the present invention is thus to provide a motor driveapparatus cable of accurately estimating demagnetization of a permanentmagnet motor.

According to the present invention, the motor drive apparatus includesan estimation unit and an operation handling unit. The estimation unitestimates an amount of demagnetization of a permanent magnet motor basedon a voltage control amount of the q axis applied in a case where thepermanent magnet motor is controlled using a d-q axis transformation.The operation handling unit limits operation of the permanent magnetmotor when the amount of demagnetization estimated by the estimationunit is greater than a predetermined value.

Preferably, the motor drive apparatus further includes a converter. Theconverter changes an input voltage necessary for driving the permanentmagnet motor. The estimation unit corrects the estimated amount ofdemagnetization according to the level of the input voltage.

Preferably, the estimation unit estimates the amount of demagnetizationby comparing the voltage control amount of the q axis to be controlledwith a reference value.

Preferably, the estimation unit estimates the amount of demagnetizationbased on a difference between a reference value and the voltage controlamount of the q axis to be controlled.

Preferably, the estimation unit holds, in the form of a map, thereference values correlated with at least two revolution numbers toextract the reference value and estimate the amount of demagnetization.

Preferably, the reference value is the voltage control amount of the qaxis when no demagnetization of the permanent magnet motor occurs.

With the motor drive apparatus of the present invention, the amount ofdemagnetization is estimated based on the voltage control amount of theq axis applied when the permanent magnet motor is controlled using thed-q axis transformation, namely the armature flux linkage in thedirection of the q axis among armature flux linkages emitted frompermanent magnets. Then, if the estimated amount of demagnetization islarger than a predetermined value, the operation of the permanent magnetmotor is limited.

The present invention can in this way estimate the amount ofdemagnetization accurately and, based on the estimated amount ofdemagnetization, the permanent magnet motor can appropriately behandled.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic block diagram of a motor drive apparatus accordingto an embodiment of the present invention.

FIG. 2 is a circuit diagram of a converter shown in FIG. 1.

FIG. 3 is a circuit diagram of an inverter shown in FIG. 1.

FIGS. 4A and 4B conceptually illustrate how to calculate an amount ofdemagnetization of a permanent magnet motor shown in FIG. 1.

FIG. 5 conceptually shows a map held by a map holding unit shown in FIG.1.

FIG. 6 is a timing chart of voltage commands of the converter shown inFIG. 1.

BEST MODES FOR CARRYING OUT THE INVENTION

Embodiments of the present invention are hereinafter described in detailwith reference to the drawings. It is noted here that like componentsare denoted by like reference characters and the description thereof isnot repeated.

Referring to FIG. 1, according to an embodiment of the presentinvention, a motor drive apparatus 100 includes a DC power supply 10,voltage sensors 11 and 12, a converter 20, a capacitor 30, an inverter40, electric-current sensors 50, a rotational position sensor 70, andcontrol devices 80 and 90.

Converter 20 is connected between DC power supply 10 and capacitor 30.Capacitor 30 is connected between a power supply line 1 and a groundline 2.

Voltage sensor 11 detects a DC voltage Vb which is output from DC powersupply 10 to output the detected voltage to control device 90. Voltagesensor 12 detects a terminal-to-terminal voltage Vm of capacitor 30 tooutput the detected voltage Vm to control devices 80 and 90.

Converter 20 increases DC voltage Vb from DC power supply 10 in responseto signal PWM1 from control device 90 to apply the increased voltage tocapacitor 30. Capacitor 30 then smoothes the DC voltage from converter20 to apply the smoothed DC voltage to inverter 40.

Inverter 40 receives the DC voltage via capacitor 30 to convert the DCvoltage into an AC voltage in response to signal PWM2 from controldevice 80 and thereby drive a permanent magnet motor 60,Electric-current sensors 50 detect motor currents Iu and Iv flowingthrough permanent magnet motor 60 to output the detected motor currentsIu and Iv to control device 80. In FIG. 1, there are provided only twocurrent sensors 50 for the following reason. It is supposed here thatpermanent magnet motor 60 is a three-phase motor. Then, motor currentsIu and Iv flowing through two phases respectively may be detected tocalculate, from the detected motor currents Iu and Iv, motor current Iwflowing through the remaining phase. Therefore, if these motor currentsIu, Iv and Iw flowing through respective three phases are to be detectedseparately, three current sensors 50 may be provided.

Permanent magnet motor 60 which is the three-phase motor includes U, Vand W-phase coils as stator coils.

Rotational position sensor 70 detects a rotational position of a rotorof permanent magnet-motor 60 to output a sensor value θ indicative ofthe detected rotational position to control device 80.

Control device 80 includes a revolution number detection unit 81, athree-phase to two-phase transformation unit 82, a current commandgeneration unit 83, subtracters 84 and 85, a PI control unit 86, atwo-phase to three-phase transformation unit 87, a PWM generation unit88, a map holding unit 89, and a demagnetized state calculation unit 91.

Revolution number detection unit 81 receives sensor value θ fromrotational position sensor 70 to detect a motor revolution number MEN(number of revolutions of the motor) based on the received sensor valueθ. Revolution number detection unit 81 then outputs this motorrevolution number MRN to current command generation unit 83, map holdingunit 89, demagnetized state calculation unit 91 and control device 90.

Three-phase to two-phase transformation unit 82 receives respectivemotor currents Iu and Iv from two current sensors 50, 50. Based on motorcurrents-Iu and Iv, three-phase to two-phase transformation unit 82calculates motor current Iw(=−Iu−Iv).

Then, three-phase to two-phase transformation unit 82 performsthree-phase to two-phase transformation on motor currents Iu, Iv and Iwusing sensor value θ from rotational position sensor 70. Specifically,three-phase to two-phase transformation unit 82 substitutes motorcurrents Iu, Iv and Iw and sensor value θ into the following expressionto calculate current values Id and Iq.

$\begin{matrix}{\begin{bmatrix}{Id} \\{Iq}\end{bmatrix} = {{\frac{2}{3}\begin{bmatrix}{{- \cos}\;\theta} & {{- \cos}\mspace{11mu}\left( {\theta - {\frac{2}{3}\pi}} \right)} & {{- \cos}\mspace{11mu}\left( {\theta + {\frac{2}{3}\pi}} \right)} \\{\sin\;\theta} & {\sin\mspace{11mu}\left( {\theta - {\frac{2}{3}\pi}} \right)} & {\sin\mspace{11mu}\left( {\theta + {\frac{2}{3}\pi}} \right)}\end{bmatrix}}\begin{bmatrix}{Iu} \\{Iv} \\{Iw}\end{bmatrix}}} & (1)\end{matrix}$

More specifically, using sensor value θ, three-phase to two-phasetransformation unit 82 transforms respective three-phase motor currentsIu, Iv and Iw flowing through respective three-phase coils ofpermanent-magnet motor 60 into current values Id and Iq. Three-phase totwo-phase transformation unit 82 then outputs the calculated currentvalues Id and Iq to subtracters 84 and 85 respectively.

Current command generation unit 83 receives a torque command value TRfrom an ECU (Electrical Control Unit) provided outside motor driveapparatus 100, receives motor revolution number MRN from revolutionnumber detection unit 81 and receives voltage Vm from voltage sensor 12.Then, current command generation unit 83 generates, based on thesetorque command value TR, motor revolution number MRN and voltage Vm,current commands Id* and Iq* for outputting the torque indicated bytorque command value TR, outputs the generated current command Id* tosubtracter 84 and map holding unit 89 and outputs the generated currentcommand Iq* to subtracter 85 and map holding unit 89.

Subtracter 84 calculates deviation ΔId between current command Id* andcurrent value Id to output the calculated deviation ΔId to PI controlunit 86. Subtracter 85 calculates deviation ΔMq between current commandIq* and current value Iq to output the calculated deviation ΔIq to PIcontrol unit 86.

PI control unit 86 uses a PI gain for deviations ΔId and ΔIq tocalculate voltage control amounts Vd and Vq for adjusting the motorcurrent, outputs the calculated voltage control amount Vd to two-phaseto three-phase transformation unit 87 and outputs the calculated voltagecontrol amount Vq to two-phase to three-phase transformation unit 87 anddemagnetized state calculation unit 91.

Two-phase to three-phase transformation unit 87 performs two-phase tothree-phase transformation on voltage control amounts Vd and Vq from PIcontrol unit 86 using sensor value θ from rotational position sensor 70.Specifically, two-phase to three-phase transformation unit 87substitutes voltage control amounts Vd and Vq from PI control unit 86and sensor value θ from rotational position sensor 70 into the followingexpression to calculate voltage control amounts Vu, Vv and Vw to beapplied to the three-phase coils of permanent magnet motor 60.

$\begin{matrix}{\begin{bmatrix}{Vu} \\{Vv} \\{Vw}\end{bmatrix} = {\begin{bmatrix}{{- \cos}\;\theta} & {\sin\;\theta} \\{{- \cos}\;\left( {\theta - {\frac{2}{3}\pi}} \right)} & {{\sin\;\left( {\theta - {\frac{2}{3}\pi}} \right)}\;} \\{{- \cos}\;\left( {\theta + {\frac{2}{3}\pi}} \right)} & {\sin\;\left( {\theta + {\frac{2}{3}\pi}} \right)}\end{bmatrix}\begin{bmatrix}{Vd} \\{Vq}\end{bmatrix}}} & (2)\end{matrix}$

In other words, using sensor value θ, two-phase to three-phasetransformation unit 87 transforms voltage control amounts Vd and Vqapplied to the d axis and the q axis into voltage control amounts Vu, Vvand Vw applied to the three-phase coils of permanent magnet motor 60.

Then, two-phase to three-phase transformation unit 87 outputs voltagecontrol amounts Vu, Vv and Vw to PWM generation unit 88.

PWM generation unit 88 generates signal PWM based on voltage controlamounts Vu, Vv and Vw and voltage Vm from voltage sensor 12 to outputthe generated signal PWM to inverter 40. More specifically, PWMgeneration unit 88 sets the amplitude and width of a pulse according tothe level of voltage Vm to generate signal PWM2. Here, if the level ofvoltage Vm is relatively higher, PWM generation unit 88 makes theamplitude of the pulse relatively higher while making the width thereofrelatively smaller to generate signal PVWM2.

Map holding unit 89 holds a map showing a voltage control amount Vq_mapof the q axis measured for each pair of current commands Id* and Iq*,and the control amount is correlated with at least two motor revolutionnumbers. This voltage control amount Vq_map is a voltage control amountof the q axis in a case where permanent magnet motor 60 is notdemagnetized.

Map holding unit 89 receives current commands Id* and Iq* from currentcommand generation unit 83 and receives motor revolution number MRN fromrevolution number detection unit 81 to extract voltage control amountVq_map correlated with these motor revolution number MRN and currentcommands Id* and Iq* and output the extracted control amount todemagnetized state calculation unit 91.

Demagnetized state calculation unit 91 calculates, according to a methodhereinlater described, an amount of demagnetization of permanent magnetmotor 60 based on voltage control amount Vq of the q axis from PIcontrol unit 86, voltage control amount Vq_map from map holding unit 89and motor revolution number MRN from revolution number detection unit81, and limits the current to be flown to permanent magnet motor 60 ormotor revolution number MRN of permanent magnet motor 60 or outputsoperation signal OPE for outputting a warning to the outside if thecalculated amount of demagnetization is greater than a predeterminedvalue.

Moreover, demagnetized state calculation unit 91 corrects, with a methodhereinlater described, the calculated amount of demagnetizationaccording to the level of voltage Vm from voltage sensor 12.

Control device 90 generates signal PWM1 for controlling converter 20based on torque command value TR from the external ECU, DC voltage Vbfrom voltage sensor 11, voltage Vm from voltage sensor 12 and motorrevolution number MRN from revolution number detection unit 81, andoutputs the generated signal PWM1 to converter 20.

More specifically, control device 90 calculates a voltage command forconverter 20 based on torque command value TR and motor revolutionnumber MRN to generate, based on the calculated voltage command, DCvoltage Vb and voltage Vm, signal PWM1 for setting voltage Vm to thevoltage command.

FIG. 2 is a circuit diagram of converter 20 shown in FIG. 1. Referringto FIG. 2, converter 20 includes NPN transistors Q1 and Q2, diodes D1and D2 and a reactor L1. NPN transistors Q1 and Q2 are connected inseries between power-supply line 1 and ground line 2. Reactor L1 has oneend connected to the intermediate point between NPN transistor Q1 andNPN transistor Q2 and the other end connected to the positive electrodeof DC power supply 10. Between respective collectors and emitters of NPNtransistors Q1 and Q2, diodes D1 and D2 for allowing current to flowfrom the emitter to the collector of the transistors each are connectedrespectively.

FIG. 3 is a circuit diagram of inverter 40 shown in FIG. 1. Referring toFIG. 3, inverter 40 includes a U phase arm 15, a V phase arm 16 and a Wphase arm 17. U phase arm 15, V phase arm 16 and W phase arm 17 areprovided in parallel between power-supply line 1 and ground line 2.

U phase arm 15 is comprised of NPN transistors Q3 and Q4 connected inseries, V phase arm 16 is comprised of NPN transistors Q5 and Q6connected in series, and W phase arm 17 is comprised of NPN transistorsQ7 and Q8 connected in series. Between respective collectors andemitters of NPN transistors Q3-Q8, diodes D3-D8 for allowing current toflow from the emitter to the collector of NPN transistors Q3-Q8 each areconnected respectively.

The intermediate point of the phase arms each of inverter 40 isconnected to an end of the phase coils each of permanent magnet motor60. In other words, the end of the U phase coil of permanent magnetmotor 60 is connected to the intermediate point between NPN transistorsQ3 and Q4, the end of the V phase coil thereof is connected to theintermediate point between NPN transistors Q5 and Q6 and the end of theW phase coil thereof is connected to the intermediate point between NPNtransistors Q7 and Q8.

FIGS. 4A and 4B conceptually illustrate how to calculate an amount ofdemagnetization of permanent magnet motor 60 shown in FIG. 1. Thevoltage generated by magnets of permanent magnet motor 60 appears in thedirection of the q axis.

Thus, according to the present invention, the amount of demagnetizationof permanent magnet motor 60 is calculated based on voltage controlamount Vq of the q axis that is applied when permanent magnet motor 60is controlled using the d-q axis transformation.

In the case where permanent magnet motor 60 is controlled with the d-qaxis transformation, the voltage of the q axis is represented by thefollowing voltage equation:Vq=ωΦ−ωLdId+RIq  (3)where ω is rotational angular velocity, Φ is armature flux linkage bypermanent magnets, Ld is inductance of the q axis, R is armatureresistance, Id is d axis component of armature current and Iq is q axiscomponent of the armature current.

In equation (3), the term ωLdId is used for field-weakening control.

FIG. 4A shows a case where no demagnetization occurs while FIG. 4B showsa case where demagnetization occurs. If demagnetization does not occur,the armature flux linkage is Dc and the voltage control amount of the qaxis is Vqc. Then, in the case where no demagnetization occurs, thefollowing expression is established.Vqc=ωΦc−ωLdId+RIq   (4)If demagnetization occurs, the armature flux linkage is Φ1 and thevoltage control amount of the q axis is Vq1. Then, in the case wheredemagnetization occurs, the following expression is established.Vq1=ωΦ1−ωLdId+Riq  (5)Expression (5) is then subtracted from expression (4):Vqc−Vq1=ω(Φc−Φ1)Φc−Φ1=(Vqc−Vq1)/ω  (6).

There is a relation Φ1<Φc in the case where demagnetization occurs sothat the left side of expression (6) represents an amount of change inarmature flux linkage, namely an amount of demagnetization.

Therefore, the right side of expression (6) can be calculated todetermine the amount of demagnetization.

According to the present invention, voltage control amount Vqc of the qaxis in the case where no demagnetization occurs is measured in advancefor each pair of current commands Id* and Iq* and the resultant valueVq_map is held in the form of the map. Then, the measured value Vq_map,voltage control amount Vq1 to be controlled and rotational angularvelocity ω are substituted into expression (6) to determine the amountof demagnetization Φc−Φ1.

If the determined amount of demagnetization Φc−Φ1 is a positive value,demagnetization of permanent magnet motor 60 occurs. If the determinedamount of demagnetization Φc−Φ1 is zero, no demagnetization of permanentmagnet motor 60 occurs.

Thus, according to the present invention, the amount of demagnetizationis calculated based on voltage control amount Vq of the q axis incontrolling permanent magnet motor 60 through the d-q axistransformation. Then, from the calculated amount of demagnetization, itis determined whether or not demagnetization of permanent magnet motor60 occurs.

FIG. 5 conceptually shows the map held by map holding unit 89 shown inFIG. 1. Referring to FIG. 5, this map MAP is comprised of a plurality ofvoltage control amounts Vq_map each located at a point of intersectionbetween a line representing a motor revolution number and a linerepresenting a torque. The white circles in FIG. 5 each representvoltage control amount Vq_map.

This map MAP includes voltage control amounts Vq_map for at least twomotor revolution numbers MRN1 and MRN 2.

Regarding permanent magnet motor 60, the torque is a function betweenthe d axis component Id and the q axis component Iq of the armaturecurrent, so that the torque shown in FIG. 5 represents the d axiscomponent Id and the q axis component Iq of the armature current.Therefore, the fact that voltage control amount Vq_map is located at thepoint of intersection between a line representing a motor revolutionnumber and a line representing a torque means that voltage controlamount Vq_map is located at the point of intersection between the linerepresenting the motor revolution number and respective linesrepresenting the d axis component Id and the q axis component Iq of thearmature current. In other words, map MAP is comprised of voltagecontrol amounts Vq_map correlated with motor revolution numbers MRN1,MRN2 and the d axis component Id and the q axis component Iq of thearmature current.

Referring again to FIG. 1, map holding unit 89 receives current commandsId* and Iq* from current command generation unit 83 and receives motorrevolution number MRN from revolution number detection unit 81. Asdiscussed above, map MAP is comprised of voltage control amounts Vq_mapcorrelated with motor revolution numbers MRN1 and MRN2 and d axis and qaxis components Id and Iq of the armature current. Then, map holdingunit 89 extracts from map MAP voltage control amount Vq_map located atthe point correlated with current commands Id* and Iq* from currentcommand generation unit 83 and motor revolution number MRN fromrevolution number detection unit 81 to output the extracted voltagecontrol amount Vq_map to demagnetized state calculation unit 91.

Demagnetized state calculation unit 91 receives voltage control amountVq from PI control unit 86, receives voltage control amount Vq_map frommap holding unit 89 and receives motor revolution number MRN fromrevolution number detection unit 81. Then, demagnetized statecalculation unit 91 calculates rotational angular velocity ω based onmotor revolution number MRN from revolution number detection unit 81 andsubstitutes the calculated rotational angular velocity co and voltagecontrol amounts Vq_map and Vq into expression (6). In this case, voltagecontrol amount Vq_map is substituted for Vqc of expression (6) andvoltage control amount Vq is substituted for Vq1 of expression (6).

If the result of calculation Φc−Φ1 is larger than a predetermined value,demagnetized state calculation unit 91 determines that demagnetizationof permanent magnet motor 60 occurs to generate operation signal OPE andoutput this signal to the external ECU. In contrast, if the result ofcalculation Φc−Φ1 is equal to or smaller than the predetermined value,demagnetized state calculation unit 91 determines that nodemagnetization of permanent magnet motor 60 occurs.

In this way, demagnetized state calculation unit 91 calculates an amountof change in armature flux linkage based on voltage control amountVq_map which is measured in advance when no demagnetization of permanentmagnet motor 60 occurs as well as voltage control amount Vq to becontrolled and determines, from the result of the calculation, whetheror not demagnetization of permanent magnet motor 60 occurs.

If demagnetization of permanent magnet motor 60 occurs, sensor value θfrom rotational position sensor 70 reflects the demagnetization andaccordingly, three-phase to two-phase transformation unit 82 transformsmotor currents Iu, Iv and Iw into current values Id and Iq with sensorvalue θ reflecting the demagnetization. Current values Id and Iq arethus influenced by demagnetization.

PI control unit 86 then uses a PI gain for deviations ΔId(=Id*−Id) andΔIq(=Iq*−Iq) to calculate voltage control amounts Vd and Vq foradjusting the motor current, so that voltage control amount Vq is avalue reflecting demagnetization.

Accordingly, with the result of calculation Φc−Φ1 performed throughsubstitution of voltage control amounts Vq_map and Vq into expression(6), whether or not demagnetization of permanent magnet motor 60 occurscan be determined.

Demagnetized state calculation unit 91 corrects, according to the inputvoltage of inverter 40, namely the level of output voltage Vm ofconverter 20, the amount of demagnetization Φc−Φ1 which is calculated bythe above-described method.

FIG. 6 is a timing chart of voltage commands of converter 20 shown inFIG. 1. It is herein described above that voltage control amount Vq_mapin the case where no demagnetization of permanent magnet motor 60 occursis measured in advance. The measured voltage control amount Vq_mapincludes the dead time of NPN transistors Q3-Q8 that are components ofinverter 40.

Referring to FIG. 6, when the DC voltage applied to inverter 40 is 500V, the voltage command of the q axis, namely voltage control amountVq_map, is represented by signal PL1. Signal PL1 is a pulse signal withwidth W1 and height H1. This signal PL1 includes dead time D1. Dead timeD1 has the same height H1 as that of signal PL1 and width w.

When the DC voltage applied to inverter 40 decreases to 250 V, thevoltage command of the q axis, namely voltage control amount Vq_map, isrepresented by signal PL2. Signal PL2 is a pulse signal with width W2and height H2. Since the DC voltage applied to inverter 40 decreasesfrom 500 V to 250 V, the width and height are those values representedrespectively by width W2=2×W1 and height H2=(H1)/2.

Then, the dead time which should essentially be included in signal PL2is dead time D2 having height H2 and width w. However, with voltagecontrol amount Vq_map being measured at the DC voltage of 500 V, signalPL2 has the same dead time D1 as that of signal PL1 if no dead timecorrection is made for addressing the decrease in DC voltage applied toinverter 40. In other words, signal PL2 includes an extra dead time D3in addition to dead time D2 which should essentially be included.

Accordingly, if the DC voltage applied to inverter 40 decreases, voltagecontrol amount Vq_map has to be corrected by, removing the extra deadtime D3. Moreover, if the DC voltage applied to inverter 40 increases,voltage control amount Vq_map has to be corrected by adding the shortagedead time.

Then, demagnetized state calculation unit 91 corrects voltage controlamount Vq_map from map holding unit 89 by expressions (7) and (8)according to the level of voltage Vm from voltage sensor 12.Vq_map_(—) ad=Vq_map±Vdead_(—) q  (7)Vdead_(—) q=(Vmi−Vmnf)*(Di)*(fc)*cos β*(3)^(1/2)  (8)where Vmi is input voltage to inverter 40 in measuring voltage controlamount Vq_map, Vmf is input voltage to inverter 40 under control, Di isdead time in measuring voltage control amount Vq_map, fc is switchingfrequency of inverter 40, and P is angle formed by the q axis and acurrent vector.

In expression (7), the sign “−” in the sign “±” indicates a decrease inDC voltage which is input to inverter 40 and the sign “+” thereinindicates an increase in DC voltage input to inverter 40.

Demagnetized state calculation unit 91 then substitutes the correctedvoltage control amount Vq_map_ad, voltage control amount Vq to becontrolled and rotational angular velocity ω into expression (6) tocalculate the amount of demagnetization Φc−Φ1.

In this case, since the amount of demagnetization Φc−Φ1 is calculatedusing the corrected voltage control amount Vq_map_ad, the calculation ofthe amount of demagnetization Φc−Φ1 with the corrected voltage controlamount Vq_map_ad corresponds to correction of the amount ofdemagnetization Φc−Φ1.

In other words, demagnetized state calculation unit 91 corrects theamount of demagnetization Φc−Φ1 according to the level of the inputvoltage to inverter 40. It is noted that the correction of the dead timeaccording to the input voltage can be made by providing Vq_mapscorrelated with respective voltages.

As motor drive apparatus 100 includes converter 20 as shown in FIG. 1,the level of voltage Vm applied to inverter 40 varies depending on theoutput torque of permanent magnet motor 60.

It is thus advantageous that the amount of demagnetization is correctedaccording to the level of the DC voltage applied to inverter 40 in termsof accurate determination of the amount of demagnetization for motordrive apparatus 100 having converter 20.

If the switching frequency of inverter 40 changes, the influence of thedead time accordingly changes. Therefore, according to the presentinvention, voltage control amount Vq_map may also be corrected if theswitching frequency of inverter 40 under control changes from theswitching frequency of inverter 40 at the time when voltage controlamount Vq_map is measured.

As discussed above, demagnetized state calculation unit 91 calculatesthe difference between voltage control amount Vq_map of the q axis inthe case where no magnetization of permanent magnet motor 60 occurs andvoltage control amount Vq to be controlled that is calculated by PIcontrol unit 86 to estimate the amount of demagnetization Φc−Φ1.According to the present invention, voltage control amount Vq to becontrolled may be compared with voltage control amount Vq_map(corresponding to “reference value”) to determine whether or notdemagnetization of permanent magnet motor 60 occurs according to theresult of the comparison.

In this case, demagnetized state calculation unit 91 determines thatdemagnetization of permanent magnet motor 60 occurs if voltage controlamount Vq is smaller than voltage control amount Vq_map and determinesthat no demagnetization of permanent magnet motor 60 occurs if voltagecontrol amount Vq is equal to voltage control amount Vq_map.

Motor drive apparatus 100 described above is mounted on a hybridvehicle. If demagnetization of permanent magnet motor 60 occurs, theexternal ECU instructs control device 80 to stop permanent magnet motor60 according to operation signal OPE from demagnetized state calculationunit 91 and accordingly performs control in such a manner that thevehicle-runs with the engine. The hybrid vehicle can thus be run safely.

It is seen from the above that accurate estimation of the amount ofdemagnetization of permanent magnet motor 60 is particularly effectiveif motor drive apparatus 100 is mounted on a hybrid vehicle.

“Estimation means” for estimating the amount of demagnetization ofpermanent magnet motor 60 is comprised of map holding unit 89 anddemagnetized state calculation unit 91.

“Operation handling means” for limiting the operation of permanentmagnet motor 60 is implemented by a function of demagnetized statecalculation unit 91 of outputting operation signal OPE if the calculatedamount of demagnetization is larger than a predetermined value, amongseveral functions of demagnetized state calculation unit 91.

Moreover, while it is described above that voltage control amount Vq_mapis extracted according to current commands Id* and Iq*, the presentinvention is not limited to this and voltage control amount Vq_map maybe extracted according to currents Id and Iq detected by current sensors50 and undergo transformation by three-phase to two-phase transformationunit 82.

Although the present invention has been described and illustrated indetail, it is clearly understood that the same is by way of illustrationand example only and is not to be taken by way of limitation, the spiritand scope of the present invention being limited only by the terms ofthe appended claims.

INDUSTRIAL APPLICABILITY

The present invention is applied to a motor drive apparatus capable ofaccurately estimating demagnetization of a permanent magnet motor.

1. A motor drive apparatus comprising: a permanent magnet motor; and acontroller that: estimates an amount of demagnetization of the permanentmagnet motor based on a voltage control amount of a q axis applied undercontrol of the permanent magnet motor using a d-q axis transformation;and limits an output of the permanent magnet motor when the estimatedamount of demagnetization is larger than a predetermined value, whereinthe controller (i) obtains a reference value that is the voltage controlamount of only the q axis among the respective voltage control amount ofthe q axis and a d axis in a case where the permanent magnet motor isnot demagnetized, according to a current and a motor revolution numberof the permanent magnet motor being controlled, and (ii) estimates theamount of demagnetization based on a comparison between the referencevalue and an actual value under the control of the voltage controlamount of only the q axis among the respective voltage control amount ofthe q axis and the d axis.
 2. The motor drive apparatus according toclaim 1, further comprising: a converter changing an input voltagenecessary for driving the permanent magnet motor, wherein the controllercorrects the estimated amount of demagnetization according to a level ofthe input voltage.
 3. The motor drive apparatus according to claim 1,wherein the controller estimates the amount of demagnetization based onwhich one of the reference value and the actual value under the controlof the voltage control amount of the q axis is larger.
 4. motor driveapparatus according to claim 3, wherein the controller holds a map thatis configured based on a relationship between the voltage control amountof the q axis and a combination of current command values of the d and qaxes and the motor revolution number that are preliminarily measured ina case where the permanent magnet motor is not demagnetized, and thecontroller obtains the reference value from the map based on presentvalues of the current command values of the d and q axes and a presentvalue of the motor revolution number.
 5. The motor drive apparatusaccording to claim 3, wherein the controller holds a map that isconfigured based on a relationship between the voltage control amount ofthe q axis and a combination of measured current values of the d and qaxes and the motor revolution number that are preliminarily measured ina case where the permanent magnet motor is not demagnetized, and thecontroller obtains the reference value from the map based on presentvalues of the measured current values of the d and q axes and a presentvalue of the motor revolution number.
 6. The motor drive apparatusaccording to claim 1, wherein the controller estimates the amount ofdemagnetization based on a difference between the reference value andthe actual value under the control of the voltage control amount of theq axis.
 7. The motor drive apparatus according to claim 6, wherein thecontroller holds a map that is configured based on a relationshipbetween the voltage control amount of the q axis and a combination ofcurrent command values of the d and q axes and the motor revolutionnumber that are preliminarily measured in a case where the permanentmagnet motor is not demagnetized, and the controller obtains thereference value from the map based on present values of the currentcommand values of the d and q axes and a present value of the motorrevolution number.
 8. The motor drive apparatus according to claim 6,wherein the controller holds a map that is configured based on arelationship between the voltage control amount of the q axis and acombination of measured current values of the d and q axes and the motorrevolution number that are preliminarily measured in a case where thepermanent magnet motor is not demagnetized, and the controller obtainsthe reference value from the map based on present values of the measuredcurrent values of the d and q axes and a present value of the motorrevolution number.
 9. The motor drive apparatus according to claim 1,further comprising an inverter, wherein the voltage control amount iscorrected by adjusting dead time of transistors in the inverter whenvoltage applied to the inverter changes.
 10. The motor drive apparatusaccording to claim 1, further comprising an inverter, wherein thevoltage control amount is corrected by adjusting dead time in measuringthe voltage control amount when voltage applied to the inverter changes.